In a typical semiconductor device, a semiconductor chip is joined to an interposer. For example, in a semiconductor device using a lead frame as an interposer, a semiconductor chip is secured to a die pad formed on the lead frame as an interposer, while the lead frame and the semiconductor chip are electrically connected to each other through a wire.
To meet recent increase in density of semiconductor chips and in the number of pins thereof, semiconductor devices having package structures called BGA (Ball Grid Array) or LGA (Land Grid Array) are often used. In these semiconductor devices, semiconductor chips on which bumps are formed are mounted on substrates as interposers by flip chip technology.
Electrode pads to which solder bumps are joined and electrode pads to which external connection terminals (solder balls or leads) are joined are formed on the front surfaces and the back surfaces, respectively, of the interposers used for BGA or LGA. The electrode pads disposed on the front surfaces and the electrode pads disposed on the back surfaces are electrically connected to each other through vias formed extending through interposer bases.
In such a package structure, a semiconductor chip and an interposer are electrically and mechanically connected through a bump, so that the mechanical joining between the semiconductor chip and the interposer is weak. To increase mechanical strength of a joint portion between the semiconductor chip and the interposer, underfill resin is provided between the semiconductor chip and the interposer.
Other than the above-described BGA and LGA, semiconductor devices of chip size package type (hereinafter referred to as CSPs), such as the one disclosed, for example, in Patent Document 1 , are known. The CSPs are packaged into substantially the same size as semiconductor chips (bare chips).
The CSPs include solder bumps or posts as external connection terminals (that are soldered to semiconductor chips), and the semiconductor chips are mounted on substrates (considered as a type of interposer) using flip chip technology. It is to be noted that the posts are soldered to electrodes on the semiconductor chips (see, for example, Japanese Patent Laid-Open Publication NO. 2002-164369).